Professor dismissed error I found in her work. I need more feedback, but the field is small

Background / My problem:

I believe to have found a substantial error in my professor's original research. After getting answers to my previous question, I emailed her about it, but she was dismissive. Of course, I could be wrong and it is very possible that I am. My professor seemed not interested at all to talk to me though, so I cannot discuss this with her further.

It is not a factual error, but an error that concerns the logic of her argument. To simplify, I think that she says that both P & -P. This is not obvious at first, and it becomes apparent only after some entangling of her whole argument.

The field is small:

Now, I do not personally know anyone who is interested this field. The field is very small and I can assume that pretty much everyone knows my professor and that my professor knows pretty much everyone too and that they talk.

What do I do now? / How do I get feedback?

Ideally I would like to get feedback from other experts. Maybe I am wrong. I am happy to be wrong, but I need to understand why. I could maybe email them, but I am not sure how responsive they would be.

Also, I am worried now that if I ask other people to have a look, my professor will hear of that. She will then know that I did not take her dismissal seriously, and am working on a paper. How would I go about this? I am worried to look like a backstabber, esp. if I email other people and say "Look, I believe I have found an error in Professor XXXX work" after my professor already told me it is not an error. If I do something like this, I would also be especially worried that should I be wrong, all of this will be very embarrassing for me.

PS: This concerns original research, not a textbook. I am in the Humanities. Please give me a chance, even if you believe that I am probably wrong,